The present invention relates to the analog waveform display of a serial digital data stream, and more particularly to a serial data cursor for providing content information about the serial digital data stream from the analog waveform display.
As the world moves more and more to serial busses, such as RS-232, Firewire, USB, etc., the need for people to observe and comprehend what is being transported over these busses is increasing. Logic analyzers are the traditional instrument for analyzing what digital data is being transported over parallel busses, but do not provide an analog waveform display of the data signal. Rather logic analyzers provide grouped data words. One type of cursor for interpreting displays of grouped data words is described in U.S. Pat. No. 6,107,989 issued Aug. 22, 2000. This patent describes an adaptive cursor that highlights on the binary display of grouped data words those bits that correspond to particular segments of a predefined protocol, i.e., when the cursor is placed at one bit position in the grouped data words, all bits that relate to the segment in which the cursor is located are highlighted and the corresponding name and value of the segment may be alpha-numerically displayed. However there is no comparable ability provided for analyzing analog waveforms of serial digital data streams.
Oscilloscopes do a fine job of capturing and displaying analog waveforms representing what is occurring at the physical layer, but do little to assist with the understanding of what information is being transported over digital data busses. Oscilloscopes now are incorporating hardware that triggers on specific serial analog patterns in a serial digital data stream, such as that disclosed in U.S. Pat. No. 5,214,784 issued May 25, 1993 entitled “Sequence of Events Detector for Serial Digital Data Which Selectively Outputs Match Signal in the Series Which Defines Detected Sequence.” This hardware provides a way to continuously monitor serial digital data in analog form and precisely define the behavior that it must exhibit in order to qualify as the sequence of events that a user wants to detect. When a sequence in the serial digital data stream matches the user specified sequence, then a trigger is generated and the serial digital data stream is captured for processing/display as an analog waveform. However there is no information provided above the physical layer as to the information content of the serial digital data stream represented by such captured analog waveform.
What is desired is a serial data cursor that assists a user in understanding from an analog waveform display what information content is being represented by a corresponding serial digital data stream.